Electrical Overstress (EOS) is considered as the exposure of a device or an integrated circuit (IC) to a current or voltage beyond its absolute maximum ratings. EOS can occur due to voltage overshoots resulting in high destructive currents.
One type of EOS is Electrostatic Discharge (ESD), which is known as transfer of electrostatic charge between bodies or surfaces at different electrostatic potential. ESD can happen due to sudden discharge of charge from a charged body. The ESD occurs when differently-charged objects are brought close together or when the dielectric between them breaks down, often creating a visible spark. ESD is a high current event in the typical range of 0.1 A to 30 A in a very short period of time from 1 ns to 200 ns.
Another type of EOS relates to fast transient voltage surges. The most intense transient relate to lightning and industrial surges. Transient overvoltage events are usually of short duration, from several microseconds to a few milliseconds, but longer than ESD events. Transient voltage surges waveforms can be oscillatory or impulsive. The waveforms typically have a rising wavefront usually on the order of 0.5 μs to 10 μs. Transient over-voltages may range from 1 kV to 50 kV.
Avalanche diodes are commonly used for ESD protection, whereas transistor structures with a snap-back (negative differential resistance region) are used for reduced clamping voltages. Silicon Controlled Rectifier (SCR) or thyristor are used for special purposes where even lower clamping voltages are needed because of the very low holding voltage after latch-up. Up to now SCR are used for on-chip ESD protection because of their high robustness per area. Because of their area efficiency and low clamping voltage during on-state, a thyristor can also be used as discrete protection device for system level ESD.